1. Field of the Invention
The present invention relates to an endoscope system, an endoscope system processor device, an operation method for an endoscope system, and an operation method for an endoscope system processor device for calculating biological function information regarding the oxygen saturation of blood hemoglobin from an image signal obtained by imaging an observation target in a subject.
2. Description of the Related Art
In the medical field, it is common to perform diagnosis using an endoscope system including a light source device, an endoscope, and a processor device. In recent years, diagnosis of a lesion using the oxygen saturation of blood hemoglobin among pieces of biological function information has been performed. As a method of acquiring the oxygen saturation, a method is known in which first signal light and second signal light having different wavelength bands and different absorption coefficients for oxygenated hemoglobin and reduced hemoglobin are alternately emitted to the observation target and reflected light beams of the first and second signal light beams are detected by a sensor located at the distal end of the endoscope (refer to JP5302984B and JP5231511B). The ratio of signal values (hereinafter, referred to as a signal ratio) of pixels of an image signal corresponding to the reflected light of the first signal light detected by the sensor and an image signal corresponding to the reflected light of the second signal light detected by the sensor is maintained as a fixed value if there is no change in the oxygen saturation in the blood vessel. However, if there is a change in the oxygen saturation, the signal ratio is also changed accordingly. Therefore, it is possible to calculate the oxygen saturation based on the signal ratio of the image signals.
However, when the signal ratio changes due to factors other than blood hemoglobin, such as when there is dirt on the mucous membrane surface (for example, attachment of residue or opaque mucus), when artifacts appear, or when dye for coloring is used, the oxygen saturation calculation accuracy may be lowered. In the technique disclosed in JP5302984B, not only the value of the oxygen saturation but also the calculation accuracy is displayed by generating and displaying an oxygen saturation image in which the tone of pseudo color showing the oxygen saturation changes according to the calculation accuracy. More specifically, the “reliability” of the oxygen saturation is calculated based on the pixel value of the image signal, and the magnitude of the oxygen saturation is displayed by the pseudo color of blue to red in a high-reliability pixel, while the magnitude of the oxygen saturation is displayed by monochrome tone in a low-reliability pixel.